1. Field of the Invention
The present invention relates to a MEMS resonator and an electrical device using the same.
2. Description of the Related Art
Microelectromechanical systems (MEMS) are expected to be applied to many fields such as high-frequency/wireless, optics, acceleration sensors, biology and power. Since MEMS have advantages that they are small comparing with other conventional circuit components, and can be manufactured by a method that is compatible with semiconductor manufacturing methods, they allows downsizing, integration and cost reduction of an electrical device.
As home appliances and information communication devices have become common, downsizing of circuit components has been being desired. Specifically, it has been being desired that components such as resonators, filters and switches, which are externally mounted on IC (integrated circuit) chips, are downsized or embedded into the chips. Among these components, quartz resonators are used as resonators for oscillators that generate a specific signal. The quartz resonators are a circuit component that is difficult to downsize.
As a substitute for quartz resonators, MEMS resonators, which are manufactured by MEMS techniques, are supposed to be promising. A MEMS resonator is an element that generates an electrical signal having a frequency equal to the resonance frequency of mechanical oscillation of a microoscillator, and is composed of the oscillator and at least one electrode that is opposed to the oscillator in which one of the oscillator and the electrode functions an excitation electrode and the other functions as a detection electrode. The oscillator is excited when an electrostatic force is applied by a voltage amplitude of a high frequency signal input to the excitation electrode and a DC drive voltage applied to the oscillator. The distance and capacitance between the oscillator and detection electrode change according to the oscillation of the oscillator. Since a drive voltage is applied, electricity is repeatedly charged to the MEMS resonator and discharged from the MEMS resonator, and the MEMS resonator outputs an AC signal accordingly. Among a plurality of frequency components that are included in the high frequency signal, the output signal only includes a high frequency component that is equal to the resonance frequency of the mechanical oscillation of the oscillator. The MEMS resonator therefore functions as a signal frequency selective element (filter).
The MEMS resonators have the above-mentioned advantages of the MEMS. The MEMS resonators are therefore expected as an element that is supposed to greatly contribute to downsizing of resonators, comparing to conventionally used quartz resonators.
JP-A-2007-116700 discloses a method of increasing an output signal of MEMS resonators, in which p- and n-type semiconductors are used as the materials of an oscillator and electrode respectively.